Since (meth)acrylate can be cured by irradiation of active energy rays such as ultraviolet rays or electron beam, (meth)acrylate is used in a large amount as a cross-linking component in paint, ink, adhesives, optical lens, a filling agent, and a blend like a molding material, or as a reactive diluent component.
In particular, as a blending component of a hard coat paint, a multifunctional (meth)acrylate having 3 or more (meth)acryloyl groups is used in a large amount since a cured product thereof exhibits high hardness and excellent abrasion resistance.
As for the multifunctional (meth)acrylate, trimethylolpropane tri(meth)acrylate, glycerin tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, tripentaerythritol octa(meth)acrylate, and the like are known.
Those multifunctional (meth)acrylates have been manufactured by an esterification reaction between a corresponding polyhydric alcohol and a (meth)acrylic acid or a transesterification.
For manufacturing a multifunctional (meth)acrylate based on an esterification reaction, sulfonic acid such as sulfuric acid, paratoluenesulfonic acid, or methanesulfonic acid is used as a catalyst. However, to remove the corresponding sulfonic acid from a crude reaction product, which is obtained after completion of the esterification reaction, it is necessary to perform extraction washing using an aqueous alkali solution. As such, the processes are complicated and a marked decrease in productivity is observed. There is also a problem that, as part of the target multifunctional acrylate is saponified during the extracting operation, a decrease in yield is caused.
Meanwhile, for manufacturing a multifunctional (meth)acrylate based on a transesterification, it is possible to have a progress of the reaction without using sulfonic acid, and a method of using an organotin compound as a catalyst (see, Patent Literature 1), a method of using in combination a zinc compound and an organophosphorus compound as a catalyst (see, Patent Literature 2), and the like are known.
However, although those methods of using a catalyst have high yield of a multifunctional (meth)acrylate, from the viewpoint of a harmful property of catalyst, it is necessary to have a purification operation for reducing as possible the catalyst remained in a product. In particular, when a multifunctional (meth)acrylate having 3 or more (meth)acryloyl groups is manufactured by using a polyhydric alcohol having 3 or more alcoholic hydroxyl groups as a raw material, from the viewpoint that the multifunctional (meth)acrylate has extremely low vapor pressure so that it is difficult to be purified and obtained as a distillation component by distillation, a purification operation like liquid-liquid extraction needs to be performed several times and a decrease in productivity is marked due to complicated processes (see, Patent Literature 1). In addition, since there is a case in which high cost is required for detoxification of wastes that are generated in conjunction with purification, it is difficult to say that the method is an economically advantageous method.
Although a method of having a titanium compound with relatively low toxicity as a catalyst for a transesterification is known (see, Patent Literature 3), according to knowledge of the inventors of the present invention, the yield is very low when a polyhydric alcohol having 3 or more alcoholic hydroxyl groups is applied as a raw material for manufacture of a multifunctional (meth)acrylate having 3 or more (meth)acryloyl groups.